Recently there has been a dramatic increase in portable telephones. In addition there is a similar but scaled down portable telephone called the Personal Handy phone System (PHS). The portable telephone service area as well as the PHS system service area are somewhat limited to places like major roads, train stations, business areas, down town areas, department stores and residential areas.
Portable telephone systems (including PHS, hereafter they will be treated as the same) have a limited number of usable frequencies, since there are not an unlimited number of channels to assign to all the locations (such as roads, train station, business areas). Therefore, the cells that are controlled by base stations in areas where there is expected to be a relatively high volume of traffic are smaller, this design allows for comparatively efficient use of the various frequencies. However, in any given cell the amount the base station is utilized is obviously not fixed. For example, in business areas portable telephones are mostly used from 9:00 in the morning to 5:00 in the afternoon, but they are hardy used between 9:00 at night and 6:00 in the morning. On the other hand at a train station in a residential neighborhood, portable telephones are mostly used between 6:00 and 9:00 in the morning and between 5:00 and 9:00 at night. But at main terminals like Tokyo and Shinjuku stations portable telephones will be used throughout the day from 9:00 to 9:00.
The use of portable telephones at home is basically just for incoming calls between 6:00 in the evening to midnight, since outgoing calls are make using an ordinary phone, so it cannot be expected that portable telephones (especially for outgoing calls) will be used much in the home.
There is also the case where a special event causes a sudden demand on the system in an area where there is no need for such capacity. An example of this is the cell that contains Makuhari Messe; when there is an event going on at the Messe there is an unusually high use of portable telephones, but the problem is when there are no events there is hardly any use of portable telephones.
Therefore, the amount of traffic a base station receives depends upon changes in time and seas on. Currently, this results in the equipment of a base station being set up to accommodate the largest amount of traffic that is expected